1. Field of the Invention
The present invention relates to an optical recording/reproducing apparatus for recording digital data on a disk and reproducing digital data from a disk, and more particularly, to a method for detecting servo error by comparing the levels of synchronous signals recorded on the header area of a disk, an apparatus suitable for the method, a disk which guarantees the quality of a push-pull signal which is the basis of optimally controlling the servo, a method for controlling the servo of the recording/reproducing apparatus, a method for detecting a tracking error, and a method for detecting a tilt error.
2. Description of the Related Art
The quality of a signal remarkably deteriorates due to a servo error such as the tilt and detrack of a disk as recording density becomes higher not only in a disk only for reproduction such as a DVD-ROM but also in a recordable disk such as a DVD-RAM. In particular, in the recordable disk, the recording quality deteriorates due to the influence of the servo error when the servo error exists during recording and the deterioration of the quality of the signal becomes severe due to the servo error during the reproduction of a concerned part.
In a DVD-RAM disk, information is recorded on a track. The track is comprised of a land track and a groove track. The land track and the groove track alternate when the disk rotates once. The land track and the groove track are alternated in the DVD-RAM disk in order to provide a tracking guide in an initial stage and to reduce crosstalk between adjacent tracks in high density narrow tracks.
Each track is comprised of sectors having a uniform length. A pre-embossed header area is provided during the manufacturing of the disk as a means of physically dividing the sectors. The physical addresses of the sectors are recorded in the pre-embossed header area.
Each sector is comprised of a header area in which physical identification data (PID) is recorded and a data area.
FIG. 1A shows the physical shape of the land track in a DVD-RAM disk. FIG. 1B shows the waveform of a push-pull signal in the land track.
The header area is repeatedly arranged in every sector of the track. Four PIDs (PID1 through PID4) having the same value are recorded in one header area. The PID1 and the PID2 are arranged to deviate from the center of the track by a certain amount and the PID3 and the PID4 are arranged to deviate from the center of the track in a direction opposite to that of the PID1 and PID2 so that the PIDs can be correctly read even if a laser spot 25 deviates from the center of the track. Also, the arrangements of the PID1 and PID2 and the PID3 and PID4 in the land track are opposite to those in the groove track. The push-pull signal shown in FIG. 1B can be obtained in the land track.
FIG. 2A shows the physical shape of the groove track in a DVD-RAM disk. FIG. 2B shows the waveform of the push-pull signal in the groove track.
FIG. 3 shows the enlarged header area shown in FIGS. 1A and 2A. In the structure of the header area, the PID1 and PID2 and the PID3 and PID4 are arranged to deviate from the center of the track in opposite directions by a uniform amount. A vfo signal having a specified frequency for synchronizing and detecting ID and an ID signal showing the physical addresses of the sectors are recorded in the respective PIDs. The vfo signal has a recording pattern of 4T (T is a period of the clock signal).
As shown in FIG. 3, the header area is comprised of vfo133 and ID1 (PID1) 34, vfo235 and ID2 (PID2) 36, vfo337 and ID3 (PID3) 38, and vfo439 and ID4 (PID4) 40.
In FIG. 3, when the laser spot passes through the header area of the groove track, a push-pull signal RF_pp shown in FIG. 4A and a sum signal RF_sum shown in FIG. 4B are obtained. In FIG. 4A, a vfo1 signal 42 corresponds to the vfo1 signal area 33 of FIG. 3. A vfo3 signal 43 corresponds to the vfo3 signal area 37.
FIG. 5 shows the structure of an apparatus for obtaining the push-pull signal shown in FIG. 4A and the sum signal shown in FIG. 4B. In FIG. 5, reference numeral 50 denotes a photodetector divided into four sections. Reference numerals 52 and 54 denote adders. Reference numeral 56 denotes a calculator.
The apparatus shown in FIG. 5 outputs the sum signal RF_sum of signals detected by light receiving elements A through D of the photodetector divided into four, sum signals V1 and V2 of radial pairs B and C, and A and D of respective light receiving elements, and the push-pull signal RF_pp which is a subtraction signal V2xe2x88x92V1 of V1 and V2.
FIG. 10 shows a conventional technology for compensating for tilt and a method for detecting the amount of tilt by a specific pattern recorded on the track of a disk. The specific pattern coincides with the proceeding direction of the track and the center of the track and is realized in the form of a reference pit A and/or a reference pit B.
It is possible to obtain tilt information by comparing signals reproduced from the reference patterns shown in FIG. 10 with each other and to thus operate tilt compensating equipment according to the obtained tilt information or to compensate for the signals by changing the equalizer coefficient of the reproducing signal.
The reference patterns shown in FIG. 10 are located in an arbitrary position in the disk and are useful for detecting tangential tilt (tilt in a track direction).
However, in the conventional technology shown in FIG. 10, the length of the reference pattern for detecting the tilt is too short. Another pattern is necessary in order to detect the correct position of the tilt pattern. Also, radial tilt (tilt in a radial direction) cannot be detected. Since the radial tilt is larger than the tangential tilt in practice, the reference patterns are not so useful.
Since it is necessary to precisely manage the servo for the recording/reproducing apparatus to maintain an optimal recording/reproducing state, it is necessary to manage the servo error signal in high resolution.
However, the precision of the servo error signal varies depending on the disk or the reproducing apparatus. Accordingly, it is difficult to precisely manage the servo.
To solve the above problem, it is a first object of the present invention to provide an improved method of detecting a servo error.
It is a second object of the present invention to provide an apparatus for detecting a servo error suitable for the above method.
It is a third object of the present invention to provide a disk having an improved specification for maintaining the quality of a reproducing signal which is the basis of optimally controlling a servo.
It is a fourth object of the present invention to provide a method of controlling the servo of a recording/reproducing apparatus.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the first and other objects of the present invention, there is provided a method of detecting servo error of an apparatus for recording data on and reproducing data from a disk in a data area of which reference patterns having a uniform size are recorded, wherein the servo error of the recording/reproducing apparatus is detected by the ratio of the magnitude of the reference patterns recorded on at least two positions separated from each other to the magnitude of the reproducing signal corresponding to the reference patterns.
To achieve the second and other objects of the present invention, there is provided an apparatus for recording data on and reproducing data from a disk in which a recording area is divided into sectors, each sector has a header for notifying an address, each header has a first header and a second header which are recorded to deviate from the center of a track in opposite directions, and the first header and the second header each have address areas in which the addresses of sectors are recorded and synchronous signal areas in which synchronous signals for detecting the address signals recorded in the address area are recorded, the apparatus comprising a reproducing signal generator for generating a reproducing signal including sum signals V1 and V2 of radial pairs, a sum signal RF_sum, and a push-pull signal RF_pp from an optical signal reflected from the disk, a header area detector for generating a header area signal comprising a header area from the reproducing signal received from the reproducing signal generator, a first synchronous signal level detector for receiving the output of the reproducing signal generator and detecting a magnitude Ivfo1 of a synchronous signal in the first header by being synchronized with the header area signal received from the header area detector, a second synchronous signal level detector for receiving the output of the reproducing signal generator and detecting a magnitude Ivfo3 of a synchronous signal in the second header by being synchronized with the header area signal received from the header area detector, and a balance calculator for calculating the balance of the magnitude Ivfo1 of the first synchronous signal detected by the first synchronous signal level detector and the magnitude Ivfo3 of the second synchronous signal detected by the second synchronous signal level detector.
To achieve the third and other objects of the present invention, there is provided a disk in which, when the magnitude of a synchronous clock signal in a peak header is Ivfo1 and the magnitude of the synchronous clock signal in a bottom header is Ivfo3, the ratio of the magnitude of Ivfo1 to the magnitude of Ivfo3 has a predetermined restricted value.
To achieve the fourth and other objects of the present invention, there is provided a method of controlling a servo in which, when the magnitude of the synchronous clock signal in the peak header is Ivfo1 and the magnitude of the synchronous clock signal in a bottom header is Ivfo3, tilt is controlled so that the ratio of the magnitude of Ivfo1 to the magnitude of the Ivfo3 satisfies a predetermined restricted value.